Redetermination of the crystal and molecular structure of pteridine

Abstract

The crystal structure of pteridine has been redetermined from three-dimensional X-ray diffraction data and refined to a final weighted R of 0·053 for 416 independent reflections measured on a diffractometer. A satistical test with the new data indicated that the previously reported molecular orientation (T. A. Hamor and J. M. Robertson, J. Chem. Soc., 1956, 3586) can be rejected at the 0·995 level. The new molecular orientation, also confirmed by least-squares refinement of atomic occupancy factors, has led to significant shifts in observed bond distances and angles, e.g. C(4)–N(3) is increased from 1·28 to 1·35 Å, and C(2)–N(3)–C(4) decreased from 123 to 116°. The present molecular geometry is more consistent with expected values for bond distances and angles, and with the results of an MO calculation.